Oxidative dehydrogenation processes

ABSTRACT

1. A PROCESS FOR THE OXIDATIVE DEHYDROGENATION OF A DEHYDROGENATABLE HYDROCARBON FEEDSTOCK HAVING FROM 2 TO 12 CARBON ATOMS WHICH COMPRISES CONTACTING SAID FEEDSTOCK IN THE VAPOR PHASE UNDER DEHYDROGENATION CONDITIONS WITH A CATALYST CONSISTING ESSENTIALLY OF COBALT, IRON PHOSPHORUS AND COMBINED OXYGEN, WHEREIN THE PHOSPHOROUS:COBALT ATOMIC RATIO IS IN THE RANGE OF 0.01-0.5:1, AND THE OXYGEN IS PRESENT IN AN AMOUNT SUFFICIENT TO SATISFY THE VALENCE REQUIREMENTS OF SAID COBALT, IRON AND THE IRON:COBALT ATOMIC RATIO IS IN THE RANGE OF 0.01-3:1, PHOSPHROUS.

United States Patent 3,851,009 OXIDATIVE DEHYDROGENATION PROCIESESRobert S. Cichowski, San Luis Obispo, Calif., assignor to PhillipsPetroleum Company No Drawing. Original application May 6, 1971, Ser. No.140,969, now Patent No. 3,784,483. Divided and this appplication July20, 1973, Ser. No. 381,018 Int. Cl. C07c /18 US. Cl. 260-680 E 5 ClaimsAliSTRACT OF THE DISCLOSURE Organic compounds are dehydrogenated tocompounds having a higher degree of unsaturation by contacting thefeedstock in the vapor phase in the presence of an oxygencontaining gaswith a catalyst comprising cobalt in association with iron, phosphorusand oxygen. Representative of such conversions is the oxidativedehydrogenation of isopentane to isoprene and isoamylenes. Theconversion products are valuable compounds particularly useful asintermediates for the preparation of polymeric materials such assynthetic rubbers and the like.

This is a division of my copending application Ser. No. 140,969 filedMay 6, 1971, Pat. No. 3,784,483.

The present invention relates to chemical compositions and chemicalprocesses. More particularly, the invention relates to catalystcompositions, their preparation, and to catalytic processes employingsuch compositions, e.g., processes for effecting the dehydrogenation ofhydrocarbons.

Dehydrogenation process for the conversion of organic compounds tocompounds having a higher degree of unsaturation include both thermalnoncatalytic and catalytic processes. The former are characterized byundesirable side reactions, low order of conversion and yields and poorproduct selectivity. The catalytic processes are generally characterizedby the particular catalytic material employed and the conditions underwhich the processes are operated, e.g., in the absence or presence ofoxygen. While a number of such catalytic processes have attained somemeasure of commercial success, there is a continuing search to discoverand develop catalytic materials for such processes. Desirable catalystsare those materials which are more efficient in minimizing sidereactions, in improving conversion rates, in improving yields andselectivities to desired end product, and which have a lowsusceptibility to deactivation, i.e., are capable of extended periods ofoperation without regeneration, and Which can be readily regenerated toan activity approaching that of fresh catalyst. The problem constantlyfaced by those skilled in the art is the selection and characterizationof the compositions which are highly eflicient dehydrogenationcatalysts.

A great deal of recent work has been done with catalysts and catalystsystems which include halogens or halogen-releasing compounds. Suchprocesses, however, have exhibited so many disadvantages in regard toequipment corrosion and the additional expense of continuously feeding,recovering and recycling the relatively expensive halogen materials thattheir use is economically practical, large scale operations has beenelfectively precluded. Halogen-free catalysts presently appear to be themost desirable for use in dehydrogenation processes.

The present invention provides a novel catalyst and a novel process forthe conversion of organic feedstocks to products having a greater degreeof unsaturation and which have the same or lower number of carbon atomsas in the organic feed. According to this invention, organic feedstockscan be converted directly to products having a greater degree ofunsaturation by contacting $351,009 Patented Nov. 25, 1974 saidfeedstock under dehydrogenation conditions in the vapor phase in thepresence of molecular oxygen with a catalytic material comprising cobaltin association with iron, phosphorus and combined oxygen. For example,parafiinic hydrocarbons can be converted in good yields to diolefinsand/or monoolefins and monoolefins can be converted to diolefins. Theinvention is particularly suitable for the production of diolefins fromparaflins and particularly useful results are obtained by thedehydrogenation of isopentane to isoprene and isoamylenes. Theconversion products are valuable compounds useful, for example, asintermediates for the preparation of polymeric materials such assynthetic rubbers and the like.

The feedstocks which are applicable for the oxidative dehydrogenationprocesses of the present invention comprise dehydrogenatable organiccompounds having from about 2 to 12 carbon atoms per molecule and atleast one It 1-1 JHL l l grouping. Hydrocarbons are particularlyapplicable. These can be branched or unbranched and include paraiftns aswell as monoolefins, but paratfins are presently preferred. Theconversion of isopentaue to isoprene and to isoamylenes has been foundparticularly advantageous by the processes of the invention. Somespecific examples of other feeds include ethane, propane, butane,isobutane, pentane, hexane, Z-methylhexane, octane, 2,4-dimethyloctane,butene-2, Z-methylbutene-l, hexene-Z, octened, 3-methylnonene-4,dodecene-l, and the like, including mixtures thereof.

The novel catalysts of the present invention comprise cobalt associatedwith iron and phosphorus, together with suflicient oxygen to satisfy thevalence requirements of these elements. These elements are not in theelemental state but can be combined with suflicient oxygen to form oneor more neutral compounds such as cobalt phosphate, iron phosphate,cobalt oxide, iron oxide, phosphorus oxide, etc., depending upon theproportions of each element present. In general, the phosphorus shouldbe present in an amount such that the phosphoruszcobalt atomic ratio isin the range of about 0.01-0.5z1, and preferably will be in the range ofabout 0.1-0.3:1. The iron will be present in minor amounts in a rangesuch that the ironzcobalt atomic ratio is in the range of about0.01-0.3z1, and preferably will be between about 0.0 5- 0.2:1.

These catalysts can also be supported on or diluted with conventionalcatalytic carrier materials such as silica, alumina, boria, magnesia,titania, zirconia, and combinations thereof, as well as other similarconventional materials known in the art. When used, such carriermaterials will generally constitute from 40 to weight percent,preferably 60 to 90 weight percent, of the finished composite catalyst.

The catalysts of the present invention can be prepared by any suitablemethod. Conventional methods such as coprecipitation, impregnation, ordry mixing can be used. In general, any method can be used which willprovide a composition containing the above-described elements in theabove-described proportions and which will have a catalytic surface areaof at least about 1 square meter per gram. Thus, a cobalt compound, aphosphorus compound and an iron compound can be combined in any suitableway. Substantially any cobalt, phosphorus, or iron compounds can beemployed in the preparation of these catalysts so long as none of thecompounds are detrimental to the final oxidative dehydrogenationcatalyst, and essentially all of the elements in the compounds used,other than the cobalt, phosphorus and iron are removed from the finalcatalyst by prior washing or by volatilization. However, small amountsof some other elements involved in the preparation of the catalyst canbe tolerated in the final catalytic composition. For example, if alkalimetal or alkaline earth metal hydroxides are used in the procedureinvolving precipitation of the cobalt and iron, small residual amountsof such metals are not damaging. Similarly, if iron sulfate or cobaltsulfate are employed in the preparation, small residual amounts ofsulfur can be tolerated. Halogen residues, on the other hand, areundesirable and these should be minimized.

Generally, however, the preferred cobalt, phosphorus and iron compoundsare either the oxides of these elements or compounds convertible to theoxide on calcination. Some examples of these are cobalt nitrate, cobaltacetate, ferric nitrate, phosphoric acid, and the like.

A preferred catalyst preparation method is to boil a solution containingsoluble compounds of cobalt, phosphorus and iron until sufficient waterhas been removed and the mixture is a viscous, hot, syrupy liquid whichsolidifies on cooling. This largely dehydrated mixture is thenrelatively rapidly brought to a high temperature in a furnace. Forexample, the mixture is heated to 10001500 F over a period not exceedingfour hours, preferably not exceeding two hours. This relatively rapidheating to calcination temperature generally causes a foaming andexpansion of the mixture and then a solidification to a very porous andvery uniform mass having a low apparent density. After reaching thiscalcination temperature, the mass is further heated in air at 10001400 Ffor 1-24 hours.

After this calcination, the catalyst is active for use in oxidativedehydrogenation processes and can be converted into any desired form orshape, such as powder, granules, pellets, and the like.

In an alternative catalyst preparation method, solutions of suitablecobalt and iron compounds are coprecipitated by the addition of alkalimetal or alkaline earth metal hydroxides. The precipitate is thenfiltered, Washed, dried, then impregnated with a solution of a suitablephosphorus compound such as phosphoric acid. This composite is thenactivated by calcination in an oxygencontaining gas such as air at atemperature of 9001500 F. for 1-24 hours, or until the catalyst isactive for oxidative dehydrogenation.

The hydrocarbon feedstocks can be dehydrogenated according to theprocess and with the catalysts of the present invention at temperaturesin the range from about 800 to about 1300 F., preferably from about 950to about 1200 F., at any convenient pressure such as from about 7 toabout 250 p.s.i.a. and at a hydrocarbonzoxygen ratio of from about 1:1to about 1:4. The presence of steam is frequently beneficial and asteam:hydrocarbon ratio up to about 50:1 can be used. The hydrocarbonfeed rate will generally be in the range of from about 50 to about 5,000GHSV. The fixed catalyst bed is the preferred mode of contact, but othermodes, such as the fluidized bed, can also be used.

The dehydrogenation processes of this invention are ordinarily carriedout by forming a mixture, preferably a preheated mixture, of thehydrocarbon feed, the oxygencontaining gas and the steam (if used), andpassing this mixture over the catalyst at the desired temperature. Theefiiuent from the reaction zone is subjected to any suitable separationmethod to isolate and recover the desired products. Unconverted feeds orpartially converted materials can be recycled.

Generally, at least trace amounts of oxygenated products are also formedin these reactions. For example, compounds such as furan, acetaldehyde,furfural, and acetic acid can be obtained, depending upon the feed. Somecarbon oxides will be formed as well as some cracking products. In someinstances, butadiene will be formed as a by-product of the oxidativedehydrogenation of isopenta e to is p The catalyst can operate for longperiods without regeneration. However, if and when regeneration isrequired, this can be accomplished by simply halting the flow of feedhydrocarbons. Contact of the catalyst with the air and steam can bemaintained at the elevated temperature until sufficient activity isrestored.

The invention can be illustrated by the following examples.

EXAMPLE I Preparation of Catalysts An invention'Co/Fe/P/O catalyst wasprepared by mixing together 12.5 ml. of a 1 M solution of Fe(NO 187.5ml. of a 1 M solution of Co(NO and 3.5 m1. of H PO percent). The mixturewas boiled with stirring until it had the consistency of a sticky syrup.It was then transferred to a dish and calcined by heating to 1200 for 2hours, then heating at 1200 F. for 4 hours. The porous mass was thencooled and crushed to a 20-28 mesh size. The FezCo atomic ratio of thecatalyst was about 0.07:1 and the PzCo atomic ratio was about 0.27: 1.It was designated as invention Catalyst B.

In a manner essentially identical with that described above, 25 ml. of a1 M solution of Fe(NO ml. of a 1 M solution of Co(NO and 3.5 ml. of H PO(85 percent), were converted into an invention catalyst having a FezCoatomic ratio of about 0.14: 1, and a PzCo atomic ratio of about 0.28:1.It Was designated as invention Catalyst C.

In an essentially identical manner, a number of other catalysts wereprepared for comparison purposes. These had varying FezCo and PzCoratios and were designated as Catalysts C through 0. In one instance, noiron was incorporated into the catalyst at all. This was designated asCatalyst A.

EXAMPLE II Oxidative Dehydrogenation (OXD) of Isopentane Each of thecatalysts prepared in Example I was used to catalyze the oxidativedehydrogenation of isopentane to isopentenes and isoprene. The runs werecarried out in a fixed bed reactor at atmospheric pressure, at anisopentane GHSV of 1000, at an air GHSV of 5,000, and at a steam GHSV of10,000. The reactor efiluent was sampled after 15 minutes on-stream andanalyzed. The results of the analysis are shown in Table I and Table IIbelow.

TABLE I OXD of isopentane Run number 1 2 3 4 5 6 7 0.07 0.14 0.33 0.50.7 1.0 .33 0.27 0.28 0.33 0.30 0.4 0.5 atalyst A B C D E F GConversion, percen 9 26. 1 23.1 23. 2 22. 7 10.0 12. 6 Yield, percent,to-

i-Cr plus i-C 7.9 11.0 9.7 6.2 3.1 0 0 6.1 5.8 4.5 4.6 3.1 0 0 4.0 12.811.4 14.0 15.1 9.7 11.3 4.0 2.2 2.0 3.0 4.6 0.3 0.3 Modivity to monoplus diene,

pcrcent 30 7 42.3 41.8 26.8 13.6 0 0 1 Modivity is a simplifiedselectivity based on gas phase products only.

TABLE II OXD of isopentane Run number 8 9 10 11 12 13 14 15 0.06 0.150.3 0.5 1.0 3.0 3.0 7.0 0.55 0.6 0.7 0.8 1.0 1.0 2.0 2.0 H I .T K L M N0 Conversion, perccnt 24. 13.4 18.2 17.9 15.5 16.3 14.8 15.8 Yield,percent, to-

i-Gyplus 0 6.2 2.2 0 0 0 0 0 i-Cr" 4.0 2.2 0 0 0 0 0 Oxidized 10.2 14.515.2 14.3 14.6 14.5 15.2 Cracked 2.0 1.5 2.7 1.2 1.7 0.3 0.6 Modivity tomono plus diene, percent 27.6 33.6 12.2 0 0 0 0 1 Modivity is asimplified selectivity based on gas phase products only.

In Table I, it is readily seen that, in a Co/Fe/P/O catalyst, the FezCoratio is critical. A relatively small amount of Fe (Invention Runs 2 and3) results in a greater selectivity to monoolefins and diolefins thanrelatively large amounts of Fe (Control Runs 4, 5, 6 and 7) or no Fe atall (Control Run 1).

In Table II, it is also evident that the phosphorus level of a Co/Fe/P/Ocatalyst is also critical. Neither small nor large amounts of -Fe arebetter than the Fe-free catalyst of Control Run 1 if the level of P istoo high, that is, if the PzCo atomic ratio is greater than about0.5: 1. Runs 815 are control runs.

A cobalt catalyst containing neither iron nor phosphorus, that is,cobalt oxide catalyst, is very active for oxidation of hydrocarbons tocarbon oxides and has essentially no selectivity for the production ofmonoor diolefins.

While certain embodiments of the invention have been described forillustrative purposes, the invention is not limited thereto. Variousother modifications or embodiments of the invention will be apparent tothose skilled in the art in View of this disclosure. Such modificationsor embodiments are within the spirit and scope of the disclosure.

I claim:

1. A process for the oxidative dehydrogenation of a dehydrogenatablehydrocarbon feedstock having from 2 to 12 carbon atoms which comprisescontacting said feedstock in the vapor phase under dehydrogenationconditions with a catalyst consisting essentially of cobalt, iron,phosphorous and combined oxygen, wherein the phosphorouszcobalt atomicratio is in the range of 0.01-0.5:1,

6 the ironzcobalt atomic ratio is in the range of 0.013:1, and theoxygen is present in an amount suflicient to satisfy the valencerequirements of said cobalt, iron and phosphorous.

2. The process of claim 1 wherein said phosphorous: cobalt atomic ratiois in the range. of 0.10.3:1 and said ironzcobalt atomic ratio is in therange of 0.050.2:l.

3. The process of claim 2 wherein said feedstock is isopentane.

4. The process of claim 3 wherein said phosphorous: cobalt atomic ratiois 0.27:1 and said ironzcobalt atomic ratio is 0.07:1.

5. The process of claim 3 wherein said phosphorous: cobalt atomic ratiois 0.28:1 and said iron:cobalt atomic ratio is 0.14:1.

References Cited UNITED STATES PATENTS 3,270,080 8/ 1966 Christmann260-680 E 3,414,631 12/1968 Grasselli et al 260-680 E 3,642,930 2/1972Grasselli et al 260-680 E 3,702,875 11/1972 Manning et a1 260680 E3,764,632 10/1973 Takenaka et al 260-680 E PAUL M. COUGHLAN, JR.,Primary Examiner U.S. Cl. X111. 260-6833

1. A PROCESS FOR THE OXIDATIVE DEHYDROGENATION OF A DEHYDROGENATABLEHYDROCARBON FEEDSTOCK HAVING FROM 2 TO 12 CARBON ATOMS WHICH COMPRISESCONTACTING SAID FEEDSTOCK IN THE VAPOR PHASE UNDER DEHYDROGENATIONCONDITIONS WITH A CATALYST CONSISTING ESSENTIALLY OF COBALT, IRONPHOSPHORUS AND COMBINED OXYGEN, WHEREIN THE PHOSPHOROUS:COBALT ATOMICRATIO IS IN THE RANGE OF 0.01-0.5:1, AND THE OXYGEN IS PRESENT IN ANAMOUNT SUFFICIENT TO SATISFY THE VALENCE REQUIREMENTS OF SAID COBALT,IRON AND THE IRON:COBALT ATOMIC RATIO IS IN THE RANGE OF 0.01-3:1,PHOSPHROUS.